On Fri, Apr 27, 2018 at 09:39:47AM -0600, Jens Axboe wrote: > On 4/27/18 9:31 AM, Bart Van Assche wrote: > > On Fri, 2018-04-20 at 14:57 +0800, Ming Lei wrote: > >> This patches removes the expensive atomic opeation on host-wide counter > >> of .host_busy for scsi-mq, and it is observed that IOPS can be increased by > >> 15% with this change in IO test over scsi_debug. > >> > >> > >> Ming Lei (3): > >> scsi: introduce scsi_host_busy() > >> scsi: read host_busy via scsi_host_busy() > >> scsi: avoid to hold host-wide counter of host_busy for scsi_mq > >> > >> drivers/scsi/advansys.c | 8 ++++---- > >> drivers/scsi/hosts.c | 32 +++++++++++++++++++++++++++++++ > >> drivers/scsi/libsas/sas_scsi_host.c | 4 ++-- > >> drivers/scsi/megaraid/megaraid_sas_base.c | 2 +- > >> drivers/scsi/mpt3sas/mpt3sas_base.c | 4 ++-- > >> drivers/scsi/qlogicpti.c | 2 +- > >> drivers/scsi/scsi.c | 2 +- > >> drivers/scsi/scsi_error.c | 6 +++--- > >> drivers/scsi/scsi_lib.c | 23 ++++++++++++++++------ > >> drivers/scsi/scsi_sysfs.c | 2 +- > >> include/scsi/scsi_host.h | 1 + > >> 11 files changed, 65 insertions(+), 21 deletions(-)\ > > > > Hello Ming, > > > > From the MAINTAINERS file: > > > > SCSI SUBSYSTEM > > M: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxxxx> > > T: git git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi.git > > M: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx> > > T: git git://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git > > L: linux-scsi@xxxxxxxxxxxxxxx > > S: Maintained > > F: Documentation/devicetree/bindings/scsi/ > > F: drivers/scsi/ > > F: include/scsi/ > > > > Hence my surprise when I saw that you sent this patch series to Jens instead > > of James and Martin? > > Martin and James are both on the CC as well. For what it's worth, the patch > seems like a good approach to me. To handle the case that Hannes was concerned > about (older drivers doing internal command issue), I would suggest that those > drivers get instrumented to include a inc/dec of the host busy count for > internal commands that bypass the normal tagging. That means the mq case needs > to be > > blk_mq_tagset_busy_iter(&shost->tag_set, scsi_host_check_in_flight, > &in_flight); > return in_flight.cnt + atomic_read(&shost->host_busy); > > The atomic read is basically free, once we get rid of the dirty of that > variable on each IO. Actually the internal command isn't submitted via normal IO path, then it won't be completed via the normal completion path(soft_irq_done, or .timeout), so handling internal command doesn't touch the scsi generic counter of .host_busy. I have talked with Hannes a bit about this at LSFMM, looks he agreed too. Thanks, Ming
